Currently I am using a Pentax 645D with a selection of lenses from 35mm to 600mm. I have primarily been working on landscapes and environmental wildlife images (wildlife in spectacular landscapes where the animals take up anywhere from 5% to 25% of the frame). I use this for slow moving subjects in decent light. I always prefer f6.7-f11 and less then ISO 800 complimented with a suitable shutter speed for the chosen focal length. The issue though comes when the light is low or the subject is moving then the Pentax 645D becomes unsuitable for various reasons from AF, to noise, to DOF, to manual focus lenses, to camera shake... I have been compliment this with a Pentax K5 and a couple compact primes for lightweight travel and mountaineering. I have a Pentax 300mm 2.8 for the K5 from my film days but I find that this is often a bit long on the crop sensor and the AF is to sporadic.
I have been out of the loop for some time now on Canon and Nikon 35mm bodies for sometime now. Previous to this I used a Pentax 645NII and Mamiya 7. I had many years ago rented a Canon 1v and several lenses; but, as I said that was roughly 10 years ago so no real experience with Canon or Nikon.
What I am looking for is a 35mm body and lens set to compliment the 645D for when the 645D just can't perform in the conditions. The two options I see that are currently on the market are the Nikon D4 and the Canon 1Dx. Now these cameras are overkill for me in some areas. There is no way I need the burst rates that they offer or the video controls. What I see in them are moderate resolution sensors that perform superb in low light and fast/accurate/tracking AF.
I have the advantage of choosing into Nikon or Canon and can't for the life of me make up my mind as to which would best suit me. And I am by no means opposed to used previous models either.
Please whatever you do, do not tell me to drop the Pentax 645D for a Nikon D800 to cover the entire gamut. The 645D stays with me. I would be incredibly surprised if a Nikon D800 could match my Pentax 645D cropped to a 4:3 or 6:7 format with my top end glass (645FA* 120mm 4.0, 645FA* 300mm 4.0, 67M* 400mm 4.0, 645A* 600mm 5.6). I want something that isn't so demanding of lenses that can be used for a quick shot before the lion ducks his head under the bush; not something I have to carefully select the lens and aperture, set up, check focus in live view, MLU, etc. Also the Pentax K5 is not going anywhere but the 300mm 2.8 and a few other lenses will be sold. I have to retain a quality, rugged, weatherproof, light weight system.
Any thoughts or are these two cameras pretty much dead even for me as far as body, IS/VR, and glass is concerned? BTW I should mention that I am currently living in Namibia, Africa...